A filter press can comprise a plurality of membrane filter plates which are positioned slidably between a locally fixed head piece and a press plate, a hydraulic device for pressing together the membrane filter plates between the head piece and the press plate and a device for feeding a pressurized gaseous medium under pressure to a plurality of membranes of the membrane filter plates.
In the known membrane filter plates the filter cake is prematurely broken away to press the solid cake material already built up mechanically with the aid of suitable member filter plates. In this known way the desired solid content in the filter cake is attained with the appropriate sludge or waste in an economical way.
The known membrane filter plates are equipped with one or two movable membranes which are acted on by pressurized air or another gaseous medium. The apparatus operates with a gas pressure between 4 to 16 bar.
The filter plate size and the pressure to which the membranes are subject determine the requisite gas volume for the mechanical pressing out of the filter cakes.
The press components of the filter press must withstand an increased load during the mechanical pressing, i.e. an equivalent closing force must be produced reliably and repeatably. A relaxation of the closing force of the filter press during the time in which the membranes are acted on by the gas pressure can result in catastrophic consequences. Although electrical controls with corresponding safety circuits are provided a sealing element in the hydraulic plant can fail and unseal, a pressurized pipe can break or a hydraulic hose can burst. Even when a pressure relief valve is provided in the feed pipe of the pressurized medium it is not in a position to relieve the compressed gas volume in a reasonable time interval.